In recent years, a battery charge discharge control apparatus controls, as disclosed in Japanese patent document Laid-Open No. 2007-306771 (on pages 1 to 5; also available as EP2019468A1), a battery charge and discharge power for limiting a battery voltage applied to a battery within a normal voltage use range (i.e., within an allowable voltage range).
However, the battery (i.e., a secondary battery) may suffer an unintended internal composition change due to an abnormal chemical reaction when receiving an excessive charge energy that exceeds a maximum value of the SOC (State Of Charge: the remaining capacity of battery), even if the voltage between two terminals is within the normal voltage use range. The battery may also suffer the unintended internal composition change when the SOC is excessively decreased. Therefore, the charge energy should be kept in a certain range, that is, within a maximum and minimum allowable value range. The charge energy is determined based on the charge discharge current of the battery, and the use range of the charge discharge current is restricted according to the condition of the battery such as the SOC, temperature, cooling capacity and the like. Further, the battery has an internal resistance that generates heat according to the charge discharge current. Therefore, if a battery temperature increases excessively, the battery itself and/or its peripheral devices may suffer from breakage, deteriorated functionality or deformation due to the heat surpassing the heat-resistance capacity limit of the battery and the peripheral devices. In other words, a battery current should be kept within a normal current use range (i.e., within an allowable battery current range).
However, this normal current use range of the battery current may change according to the battery condition such as the SOC, battery temperature, the cooling capacity or the like, thereby inducing the battery current to surpass the allowable current range and causing the excessive heating that leads to the breakage and the like, even when the battery charge discharge power is restricted for limiting the battery voltage to be within the normal voltage use range (See FIG. 2).